As a method for backing up a source volume (for example, a business volume) of a storage device, One Point Copy (OPC) is known. OPC is executed to form, for data to be backed up, a snapshot that is data at a predetermined time. The storage device executes OPC. When receiving an OPC instruction from a user, the storage device backs up the source volume by copying all data of the source volume at the time of the reception of the OPC instruction and storing the data as a snapshot (backup data).
As advanced functions of OPC, Quick One Point Copy (QOPC), Snapshot One Point Copy (SnapOPC), SnapOPC+, and the like are known.
QOPC is a function of reflecting only updated data (differential data) in a backup volume updated before reception of a restart instruction when the restart instruction is received from a host device after all data is physically copied by OPC and the backup volume is formed. QOPC has the following two features (1) and (2).
Feature (1): After a copy process by OPC is completed, a location in a copy source volume (source volume), at which data is updated, is memorized. Upon a restart request (restart instruction), only the data at the location updated until the restart request is copied into a backup volume. In QOPC, after all data is physically copied, it is sufficient if only the difference is copied in accordance with the restart request. Thus, QOPC may achieve a reduction in the amount of data to be copied and an increase in the speed of the copy process.
Feature (2): A session is not automatically released even after the completion of the copy process by OPC and is released when stopped by software. When the session is released, the process of copying differential data is not restarted. Thus, the session is not easily released.
SnapOPC is executed, when backup data is to be formed, to back up only an updated part among data of a copy source volume and thereby reduces a physical region of a copy destination (backup destination) and the cost of copying.
SnapOPC+, which is an advanced function of SnapOPC, is executed to form a backup volume for each generation without fully copying a source volume. In SnapOPC+, data (old data) that is stored, before update, at a location targeted for update is copied into a backup volume for a corresponding generation when the source volume is updated. Specifically, in SnapOPC+, a snap data volume (SDV), which is a generation backup volume, is formed for each of generations (for example, for each day of the week), and only data of differences between the generations is copied into the SDVs.
For example, as illustrated in FIG. 10, a storage device that has SnapOPC+installed therein forms SDVs 201, 202, and 203 for Monday, Tuesday, and Wednesday on Monday, Tuesday, and Wednesday, respectively, as generation backup volumes for a source volume 100 that is a copy source. In this case, only data before update that is updated on Monday is stored in the SDV 201 for Monday; only data before update that is updated on Tuesday is stored in the SDV 202 for Tuesday; and only data before update that is updated on Wednesday is stored in the SDV 203 for Wednesday.
Thus, in the generation management by SnapOPC+, data of multiple generations may be backed up using a small physical capacity for the source volume 100. In the example illustrated in FIGS. 10 and 11, the source volume 100 and the SDVs 201 to 203 are provided as physical volumes, while the SDVs 201 to 203 store data of differences between the generations and have a smaller capacity than the source volume 100. The storage device provides, as logical volumes, backup volumes (data on Monday, data on Tuesday, and data on Wednesday) for generations to a host device 2 by combining the source volume 100 and the SDVs 201 to 203 for the generations and enables the host device 2 to access the backup volumes.
Related techniques are disclosed in, for example, Japanese Laid-open Patent Publication No. 2005-292865, Japanese Laid-open Patent Publication No. 2004-341840, and Japanese Laid-open Patent Publication No. 2010-140065.
However, in operation, data is frequently input and output between the source volume 100 and the host device 2 connected to the storage device, that is, input and output requests and data based on the input and output requests are frequently transmitted and received between the source volume 100 and the host device 2. Thus, the source volume 100 may fail or be broken at a higher rate than a backup volume formed by QOPC and the generation SDVs 201 to 203 formed by SnapOPC+. When the source volume 100 fails as illustrated in FIG. 12, backup volumes, which serve as logical volumes, for all generations fail even if the SDVs 201 to 203 do not fail. Thus, inputting and outputting to and from the host device 2 all cause an error and may affect a system operation.